Myeloid dendritic cells induce Th2 responses to inhaled antigen, leading to eosinophilic airway inflammation

Attenuation of allergen-induced responses in CCR6-/- mice is dependent upon altered pulmonary T lymphocyte activation

We have established a defect in CCR6-/- mice in response to a cockroach allergen airway challenge characterized by decreased IL-5 production, reduced CD4+ T and B cells as well as decreased eosinophil accumulation. To determine the nature of the defect in CCR6-/- mice T lymphocyte populations from allergen-sensitized wild-type mice were transferred into sensitized CCR6-/- mice. The reconstituted response was characterized by an increase in IL-5 levels, eosinophil accumulation, and serum IgE levels in recipient CCR6-/- mice. Analysis of lymphocytes from draining lymph nodes of CCR6+/+ and CCR6-/- sensitized or challenged mice demonstrated a significant decrease in IL-5 and IL-13 production in CCR6-/- mice. In contrast, the systemic response in allergen-rechallenged spleen cells demonstrated no significant alteration in allergen-induced cytokine production. Transfer of isolated splenic T lymphocytes from sensitized CCR6+/+ mice induced airway hyperresponsiveness in wild-type but not CCR6-/- naive mice, suggesting that T cells alone were not sufficient to induce airway hyperresponsiveness in CCR6-/- mice. Additional analysis demonstrated decreased CD11c+, CD11b+ and CD11c, and B220 subsets of dendritic cells in the lungs of CCR6-/- mice after allergen challenge. Using in vitro cell mixing studies with isolated pulmonary CD4+ T cells and CD11c+ cells from CCR6+/+ or CCR6-/- mice, we demonstrate alterations in both CCR6-/- T cells and CCR6-/- pulmonary APCs to elicit IL-5 responses. Altogether, the defect in CCR6-/- mice appears to be primarily due to an alteration in T cell activation, but also appears to include local pulmonary APC defects.

The interplay of dendritic cells, Th2 cells and regulatory T cells in asthma

Dendritic cells are essential for Th2 differentiation of naive CD4+ T cells in response to aeroallergens, and in recent years it has been well established that these cells play a pivotal role in the initiation phase of allergic asthma. Dendritic cells are also crucial for maintaining eosinophilic airway inflammation by controlling the recruitment and activation of primed Th2 cells in the lung. A picture is emerging wherein the balance of pathogenic Th2 cells and regulatory T cells is tuned by dendritic cells not only at the initiation but also at the effector stage of the allergic immune response.

Dendritic cells and the regulation of the allergic immune response

Studies in mouse models of asthma have revealed a critical role for airway dendritic cells in the induction of Th2 sensitization to inhaled allergens. Under some conditions, subsets of dendritic cells can also induce tolerance or Th1 responses to the same allergens, depending on the context in which the antigen is seen. This article discusses various aspects of DC biology as it relates to allergic sensitization and also provides a summary of the recent evidence that dendritic cells function beyond sensitization.

T cells modulate neutrophil-dependent acute renal failure during endotoxemia: critical role for CD28

Sepsis still represents a leading cause of acute renal failure (ARF). Both lymphocytes and neutrophils (PMN) have been proposed as crucial mediators during sepsis. For further elucidation of the mechanisms of interactions between them, a murine model of LPS-induced ARF was used. In wild-type mice (WT), LPS administration led to a strong influx of PMN into the kidney (2.8-fold greater renal myeloperoxidase activity after 24 h) and to severe ARF (3.3-fold higher plasma creatinine concentrations after 24 h). By contrast, mice that were gene deficient for CD28 (CD28(-/-)), a co-stimulatory molecule for T cell activation, exhibited only minor renal dysfunction (50% protection compared with WT) and almost no PMN recruitment. When PMN(-) depleted, both WT and CD28(-/-) developed only mild ARF, similar to untreated CD28(-/-). Flow cytometry demonstrated that CD28 was vastly expressed on CD3(+) cells but not on PMN. Injecting wild-type CD3(+) cells into CD28(-/-) before LPS injection abolished the protection seen before. At baseline, both WT and CD28(-/-) displayed similar plasma concentrations of keratinocyte-derived chemokine (KC), a growth-related oncogene 1 gene product and PMN-specific chemokine. As opposed to WT, CD28(-/-) showed a greatly attenuated increase in plasma KC 4 h after LPS (2.5- versus 138.5-fold over controls, respectively). Moreover, CD28(-/-) showed less intense upregulation of renal growth-related oncogene 1 mRNA expression. Immunohistochemistry revealed considerable PMN but no T cell infiltrates in the kidney after LPS injection. In a PMN-dependent model of endotoxemic ARF, T cells, via the CD28 pathway, modulate kidney function and renal PMN recruitment. The effect on PMN is a remote one and presumably due to altered expression of PMN-specific chemokines.

T1/ST2--an IL-1 receptor-like modulator of immune responses

Th2-associated factors such as IL-4 are involved in both the development of Th2 responses (via modulating Th2 cell differentiation) and in the effector phase of Th2 responses (via modulating macrophage activation). The IL-1 receptor-like protein ST2 (T1, Fit-1, or DER4) is expressed as a membrane-bound (ST2L) or secreted form (sST2), and has been clearly implicated as a regulator of both the development and effector phases of Th2-type responses. Here we analyze the mechanisms and therapeutic implications of the unique ability of ST2 to promote development and function of type 2 helper T cells through a positive feedback loop, as well as to act as a negative feedback modulator of macrophage pro-inflammatory function.

The role of dendritic cells in asthma

PURPOSE OF REVIEW

The central importance of respiratory tract dendritic cells in the regulation of adaptive immune responses to inhaled antigens is now well established. Dendritic cells are not merely a conduit for the transfer of antigen to regional lymph nodes, but rather function as a sophisticated information transfer system linking the airway micro-environment to the adaptive immune system. Evidence from both animal models and clinical studies points to a critical role for dendritic cells in both allergic sensitization and the pathogenesis of chronic airway inflammation.

RECENT FINDINGS

This article reviews recent information on the distribution and function of dendritic cells in healthy individuals, the responsiveness of these cells to external stimuli, and the factors regulating their activation and turnover within the lung. Animal models of allergic airway inflammation continue to shed new light on the role of lung dendritic cells in T helper 1/T helper 2 switching, and the ability of these cells to direct regulatory T-cell development and immune tolerance. Recent studies have further characterized circulating dendritic cell populations, highlighting important functional differences between dendritic cells from atopic and nonatopic individuals, and have delineated the involvement of these cells in the late phase response to inhaled allergen.

SUMMARY

Because of the immunoregulatory properties of dendritic cells, the future is likely to see a concerted effort to further define the role that these cells play in allergic sensitization, as a basis for the development of new treatments for asthma and other atopic disorders.

Essential role of lung plasmacytoid dendritic cells in preventing asthmatic reactions to harmless inhaled antigen

Tolerance is the usual outcome of inhalation of harmless antigen, yet T helper (Th) type 2 cell sensitization to inhaled allergens induced by dendritic cells (DCs) is common in atopic asthma. Here, we show that both myeloid (m) and plasmacytoid (p) DCs take up inhaled antigen in the lung and present it in an immunogenic or tolerogenic form to draining node T cells. Strikingly, depletion of pDCs during inhalation of normally inert antigen led to immunoglobulin E sensitization, airway eosinophilia, goblet cell hyperplasia, and Th2 cell cytokine production, cardinal features of asthma. Furthermore, adoptive transfer of pDCs before sensitization prevented disease in a mouse asthma model. On a functional level, pDCs did not induce T cell division but suppressed the generation of effector T cells induced by mDCs. These studies show that pDCs provide intrinsic protection against inflammatory responses to harmless antigen. Therapies exploiting pDC function might be clinically effective in preventing the development of asthma.

Activated human dendritic cells express inducible cyclo-oxygenase and synthesize prostaglandin E2 but not prostaglandin D2

Prostaglandins (PG) are well known lipid mediators with important immunoregulatory properties. While exogenous PGE2 has the ability to modulate the function and maturation of antigen presenting cells, such as dendritic cells (DC), it is not clear whether human DC have the capacity to synthesize PGE2 and other prostaglandins themselves. We therefore examined the expression of inducible cyclo-oxygenase (COX-2) by monocyte derived DC and the production of PGE2 and PGD2. Both monocyte derived DC and freshly isolated blood myeloid DC expressed little COX-2 constitutively, though COX-2 expression was rapidly but transiently upregulated in response to lipopolysaccharide stimulation. COX-2 mRNA was detectable within 1 h of LPS exposure, peaked at 4-6 h, and rapidly declined thereafter. COX-2 expression was accompanied by DC synthesis of PGE2, with peak levels present at 6-18 h post-stimulation. In contrast, PGD2 synthesis was not detected at any time point. When DC were activated with LPS in the presence of nimesulide, a COX-2 selective inhibitor, IL-10 synthesis was inhibited, indicating that endogenous prostaglandins regulate DC cytokine production. PGE2 production by DC may therefore modulate DC and T-cell function, thereby shaping the character of the immune response.

Essential role of dendritic cell CD80/CD86 costimulation in the induction, but not reactivation, of TH2 effector responses in a mouse model of asthma

BACKGROUND

Airway dendritic cells (DCs) are crucial for the generation of TH2 cells from naive T cells during sensitization and for reactivation of primed TH2 cells on allergen challenge in mouse models of asthma. It is unknown whether CD80/CD86 costimulation is necessary during both phases of the response because primed T cells rely less on costimulatory molecules compared with naive T cells.

OBJECTIVE

We sought to study the contribution of CD80/CD86 costimulatory molecules on DCs during sensitization or challenge in a mouse model of asthma.

METHODS

Naive BALB/c mice received an intratracheal injection of ovalbumin (OVA)-pulsed DCs obtained from the bone marrow of wild-type (WT) or CD80/CD86-/- mice and were subsequently challenged with OVA aerosol to address the role of costimulation during sensitization. OVA-sensitized mice received OVA-pulsed WT or CD80/CD86-/- DCs without OVA aerosol to address the role of costimulation during challenge.

RESULTS

WT DCs induced the proliferation and effector TH2 differentiation of naive OVA-specific T cells, whereas CD80/CD86-/- DCs induced only proliferation. Not surprisingly, WT DCs but not CD80/CD86-/- DCs induced sensitization to OVA in naive mice. In contrast, in OVA-sensitized mice intratracheal injection of CD80/CD86-/- OVA-pulsed DCs led to eosinophilic airway inflammation, goblet cell hyperplasia, and effector TH2 cytokine production that was not different from that seen after injection with WT OVA-DCs, even when the inducible costimulator ICOS was blocked or cytotoxic T lymphocyte-associated antigen 4 immunoglobulin was given.

CONCLUSION

CD80/CD86 costimulation on DCs is only necessary during priming of naive T cells into TH2 cells but not during restimulation of previously primed TH2 cells in the challenge phase.

Dendritic cells retrovirally overexpressing IL-12 induce strong Th1 responses to inhaled antigen in the lung but fail to revert established Th2 sensitization

It has been postulated that low-level interleukin (IL)-12 production of antigen-presenting cells is associated with the risk of developing atopic asthma. To study the relationship between IL-12 production capacity of dendritic cells (DCs) and development of T helper type 2 (Th2) responses in the lung, we genetically engineered DCs to constutively overexpress bioactive IL-12. Retrovirally mediated overexpression of IL-12 in DCs strongly polarized naive ovalbumin (OVA)-specific CD4+ T cells toward Th1 effector cells in vitro. After intratracheal injection, OVA-pulsed IL-12-overexpressing DCs failed to induce Th2 responses in vivo and no longer primed mice for Th2-dependent eosinophilic airway inflammation upon OVA aerosol challenge, readily observed in mice immunized with sham-transfected, OVA-pulsed DCs. Analysis of a panel of cytokines and chemokines in the lung demonstrated that the lack of Th2 sensitization was accompanied by increased production of the Th1 cytokine interferon-gamma (IFN-gamma), chemokines induced by IFN-gamma, and the immunoregulatory cytokine IL-10. When Th2 priming was induced using OVA/alum prior to intratracheal DC administration, DCs constitutively expressing IL-12 were no longer capable of preventing eosinophilic airway inflammation and even enhanced it. These data show directly that high-level expression of IL-12 in DCs prevents the development of Th2 sensitization. Enhancing IL-12 production in DCs should be seen as a primary prevention strategy for atopic disorders. Enhancing IL-12 production in DCs is less likely to be of benefit in already Th2-sensitized individuals.

Enrichment for a CD26hi SIRP- subset in lymph dendritic cells from the upper aero-digestive tract

Dendritic cells (DC) have been reported to migrate in afferent lymph in the steady state. However, it is unknown whether DC traffic is modulated by the nature of the drained tissue. To analyze the influence of mucosal versus cutaneous microenvironments on the constitutive DC release, we exploited a novel technique of lymph cannulation in sheep, which allowed a comparison of afferent lymph DC migrating from the head mucosae [cervical DC (CerDC)] with DC migrating from skin [prescapular DC (PresDC)]. The migration rate was lower for CerDC than for PresDC. Compared with PresDC, CerDC contained a higher proportion of the CD26hi signal regulatory protein (SIRP)- DC subset. It is interesting that cytoplasmic apoptotic DNA as well as cytokeratin-positive inclusions were primarily detected among CD26hi SIRP- DC, an observation similar to that made in rats, which leads to the suggestion that this subset was involved in self-antigen presentation and tolerance induction. After the inoculation of cholera toxin (CT) onto the oro-nasal mucosae, migration of CD26hi SIRP- and CD26lo SIRP+ DC was accelerated in lymph, indicating that the effect of CT on DC mobilization is not subset-specific. Our results show that a mucosal environment influences DC output and the relative DC subset representation in lymph. This modulation of DC traffic to lymph nodes by mucosal surfaces is likely to affect the bias of the mucosal immune responses.

Implication des cellules dendritiques en pathologie respiratoire allergique

INTRODUCTION

Dendritic cells (DCs) are able to present antigen to T lymphocytes and to orientate the immune response towards a Th1 or a Th2 type.

STATE OF THE ART

The aim of this report is to present different studies comparing DCs from allergic patients with those from healthy subjects using in vivo and in vitro experimental conditions. These studies have demonstrated that cellules dentritiquess from house dust mite allergic patients:i) take up house dust mite allergen more efficiently, ii) after stimulation by house dust mite allergen, secrete a restricted panel of cytokines and chemokines, and express characteristic co-stimulatory molecules, favoring a Th2 profile, iii) after stimulation by house dust mite allergen, induce Th2 cytokines secretion by T lymphocytes, and iv) favor an allergen-specific Th2 airway inflammatory response in an in vivo model of humanized mice.

PERSPECTIVES

Functional modulation of DC could be a new therapeutic concept in allergic airway diseases.

CONCLUSIONS

These results show phenotypic and functional specificities of DC from house dust mite allergic patients, and suggest a key-role for cellules dentritiques in the pathogenesis of allergen-dependent airway inflammatory response.

Higher prostaglandin e2 production by dendritic cells from subjects with asthma compared with normal subjects

Dendritic cells (DCs) are thought to play an important role in the pathogenesis of allergic disorders through their ability to interact with T cells to initiate and amplify helper T cell Type 2 immune responses. The mechanisms by which this occurs are not completely understood, nor is it clear whether DC function differs between normal individuals and individuals with asthma. We compared the function of DCs from 10 subjects with allergic asthma and 10 normal individuals, focusing on the production of prostaglandin E (PGE) 2, interleukin (IL)-10, and IL-12 p70, mediators that play an important role in helper T cell Type 1/Type 2 polarization. Monocyte-derived DCs were established by culturing monocytes with granulocyte-macrophage colony-stimulating factor and IL-4 for 7 days, and then stimulated with LPS plus IFN-gamma. PGE2, IL-10, and IL-12 production was evaluated by ELISA, whereas cyclooxygenase-1, and -2 messenger RNA expression was analyzed using reverse transcription-polymerase chain reaction. LPS-stimulated monocyte-derived DCs from individuals with asthma exhibited increased PGE2 and IL-10 production, but equivalent IL-12 p70 synthesis, when compared with DCs from normal subjects. Increased PGE2 synthesis by DCs from subjects with asthma was associated with an increase in cyclooxygenase-2 messenger RNA expression. These findings support the notion that DC function is significantly altered in allergic asthma.

Cysteinyl leukotrienes regulate dendritic cell functions in a murine model of asthma

Dendritic cells (DCs) act as APCs in the airway and play a critical role in allergy. Cysteinyl leukotrienes (cysLTs) synthesized from arachidonic acid are primary mediators of immediate asthmatic reaction. The aim of this study was to investigate the effects of cysLTs on Dermatophagoides farinae (Der f)-pulsed mouse myeloid DCs in inducing allergic airway inflammation in vitro and in vivo. Control DC (medium-pulsed), Der f-pulsed DC, cysLT-pulsed DC, Der f- and cysLT-pulsed DC, and Der f-pulsed and cysLT receptor antagonist (LTRA)-treated DC were prepared from murine bone marrow, and the production of cytokines ws compared. Subsequently, these DCs were intranasally instilled into another group of naive mice, followed by intranasal Der f challenge to induce allergic airway inflammation in vivo. Der f-pulsed DC produced significantly higher amounts of IL-10 and IL-12 compared with control DC. Der f- and cysLT-pulsed DC further increased IL-10 production compared with Der f-pulsed DC. In contrast, treatment of Der f-pulsed DC with LTRA increased IL-12 and decreased IL-10. Intranasal instillation of Der f-pulsed DC resulted in airway eosinophilia associated with a significant rise in IL-5 levels in the airway compared with control DC. Pulmonary eosinophilia and excess IL-5 were further enhanced in Der f- and cysLT-pulsed DC-harboring mice. In contrast, Der f-pulsed and LTRA-treated DC significantly inhibited airway eosinophilia, reduced IL-5, and increased IFN-gamma in the airway. Our results suggest that cysLTs play an important role in the development of allergic airway inflammation by regulating the immunomodulatory functions of DCs.

A rapid flow cytometric method for determining the cellular composition of bronchoalveolar lavage fluid cells in mouse models of asthma

Mouse models of allergic asthma are increasingly used to study the immunopathology of this complex disorder. The degree and type of airway inflammation is often studied by determination of differential cell counts on cytospins of bronchoalveolar lavage fluid (BALF) cells stained with May-Grünwald Giemsa, in which the separation of eosinophils (eos) from neutrophils (neutro) and of monocytes (mono) from activated T cells can be quite problematic. In this study, we compared differential cell counts based on morphological criteria on May-Grünwald Giemsa stained cytospins with a newly developed flow cytometric method. BAL fluid cells were identified based on forward and side scatter characteristics (FSC and SSC), autofluorescence of macrophages, and simultaneous one-step staining with antibodies for T cells (CD3-Cy-Chrome), B cells (B220-Cy-Chrome), eosinophils (CCR3-PE), and dendritic cells (DCs) (MHCII-FITC, CD11c-APC). The validity of this flow cytometric determination was tested by morphological analysis of flow-sorted cellular subsets. In an animal model of ovalbumin-induced asthma, this new method correlated very well with the differential counts based on cytospins. Flow cytometric determination of the cellular composition of BAL fluid in mouse models of asthma is a rapid and easy method that can replace differential cell counts based on morphology.

Why are dendritic cells important in allergic diseases of the respiratory tract?

Increasing evidence points to the role of antigen-presenting dendritic cells (DC) in regulating adaptive immune responses. DC are especially sensitive to signals derived from microbes, allergens, and the airway tissue microenvironment, can polarize naïve T-cells into either Th1 or Th2 effector cells, and are increasingly recognized as having a central role in the establishment of T-cell memory and tolerance to inhaled antigens. DC form a closely meshed network within the respiratory mucosa and are rapidly recruited from the circulation in response to a variety of proinflammatory stimuli. Studies using animal models have highlighted the role of DC in both initiation and maintenance of allergic airway inflammation. Increased numbers of airway mucosal DC are found in both allergic rhinitis and asthma, and an increasing number of investigators have highlighted important functional differences between DC from atopic and normal individuals. This article reviews recent information on the involvement of DC in the pathogenesis of allergic airway disease and the means by which DC could be exploited as targets for therapy in asthma and allergic rhinitis.

Activation of peroxisome proliferator-activated receptor-gamma in dendritic cells inhibits the development of eosinophilic airway inflammation in a mouse model of asthma

Peroxisome proliferator-activated receptors (PPARs) are activated by an array of polyunsaturated fatty acid derivatives, oxidized fatty acids, and phospholipids and are proposed to be important modulators of immune and inflammatory responses. Recently, we showed that activation of PPAR-gamma alters the maturation process of dendritic cells (DCs), the most potent antigen-presenting cells. In the present report, we investigated the possibility that, by targeting DCs, PPAR-gamma activation may be involved in the regulation of the pulmonary immune response to allergens. Using a model of sensitization, based on the intratracheal transfer of ovalbumin (OVA)-pulsed DCs, we show that rosiglitazone, a selective PPAR-gamma agonist, reduces the proliferation of Ag-specific T cells in the draining mediastinal lymph nodes but, surprisingly enough, dramatically increases the production of the immunoregulatory cytokine interleukin (IL)-10 by T cells, as compared to control mice sensitized with OVA-pulsed DCs. After aerosol challenge, the recruitment of eosinophils in the bronchoalveolar lavage fluids was strongly reduced compared to control mice. Finally, T cells from the mediastinal lymph nodes produced higher amounts of IL-10 and interferon-gamma. Inhibition of IL-10 activity with anti-IL-10R antibodies partly restored the inflammation. The specificity of the phenomenon was confirmed by treating OVA-pulsed DCs with ciglitazone, another PPAR-gamma agonist, and by using GW9662, a PPAR-gamma antagonist. Our data suggest that PPAR-gamma activation prevents induction of Th2-dependent eosinophilic airway inflammation and might contribute to immune homeostasis in the lung.

Viral-induced T helper type 1 responses enhance allergic disease by effects on lung dendritic cells

It is widely accepted that T helper type 1 (T(H)1) cytokines such as interferon-gamma (IFN-gamma) antagonize allergic diseases mediated by T(H)2 cytokines. The 'hygiene hypothesis' has also proposed that decreased childhood exposure to pathogen-derived T(H)1 cytokines may underlie the recent increased prevalence of asthma, a T(H)2-mediated disease. We show here that influenza A viral infection, which induces large amounts of intrapulmonary IFN-gamma production, unexpectedly enhanced later allergen-specific asthma and promoted dual allergen-specific T(H)1 and T(H)2 responses. Pulmonary dendritic cells obtained from the lung after viral clearance and resolution of acute inflammation conferred enhanced allergic disease and concurrent T(H)1 and T(H)2 immune responses, and these effects were dependent on IFN-gamma secreted during the acute viral infection. Thus, respiratory viral infection and the acute T(H)1 response can positively regulate T(H)2-dependent allergic pulmonary disease in vivo, at least in part, by altering pulmonary dendritic cell function.

Runx3 regulates mouse TGF-beta-mediated dendritic cell function and its absence results in airway inflammation

Runx3 transcription factor regulates cell lineage decisions in thymopoiesis and neurogenesis. Here we report that Runx3 knockout (KO) mice develop spontaneous eosinophilic lung inflammation associated with airway remodeling and mucus hypersecretion. Runx3 is specifically expressed in mature dendritic cells (DC) and mediates their response to TGF-beta. In the absence of Runx3, DC become insensitive to TGF-beta-induced maturation inhibition, and TGF-beta-dependent Langerhans cell development is impaired. Maturation of Runx3 KO DC is accelerated and accompanied by increased efficacy to stimulate T cells and aberrant expression of beta2-integrins. Lung alveoli of Runx3 KO mice accumulate DC characteristic of allergic airway inflammation. Taken together, abnormalities in DC function and subset distribution may constitute the primary immune system defect, which leads to the eosinophilic lung inflammation in Runx3 KO mice. These data may help elucidate the molecular mechanisms underlying the pathogenesis of allergic airway inflammation in humans.

Human thymic stromal lymphopoietin: a novel epithelial cell-derived cytokine and a potential key player in the induction of allergic inflammation

Allergy is the result of a complex immune cascade leading to the dysregulated production of Th2 cytokines, the generation of allergen-specific IgE-producing B cells and the subsequent activation and degranulation of mast cells upon allergen challenge. Dendritic cells (DCs) play an important role in several models of allergy, but factors instructing DCs to induce a dysregulated Th2 response are currently unknown. In this review, we present recent evidence that human thymic stromal lymphopoietin (TSLP), a novel IL-7-like cytokine, might represent an early trigger of the allergic immune cascade. TSLP-activated human DCs produce Th2-attracting chemokines but no IL-12, and induce naive CD4(+) and CD8(+) T cell differentiation into effector cells with a typical pro-allergic phenotype. TSLP is produced by human epithelial, stromal, and mast cells. It is highly expressed by the keratinocytes of atopic dermatitis but not in other types of skin inflammation. Thus, epithelial- and stromal-cell-derived TSLP might represent one of the factors initiating the allergic responses, and could be a target for a curative therapeutic approach to allergy.

Up-regulation of C5a receptor expression and function on human monocyte derived dendritic cells by prostaglandin E2

The expression of the C5a-receptor (C5aR) on dendritic cells, its regulation and function have not been well established thus far. We show that the C5aR is expressed on human monocyte-derived dendritic cells (DC) and can be down-regulated by maturation stimuli such as tumour necrosis factor-alpha (TNF-alpha), lipopolysaccharide (LPS) or CD40L and by the T helper 1-cytokine interferon-gamma (INF-gamma). Prostaglandin E2 (PGE2), a proinflammatory mediator supporting dendritic cell activation and necessary for adequate DC migration, leads to the up-regulation of C5aR expression when incubated alone and prevents down-regulation when given in combination with TNF-alpha or LPS. Stimulation of C5aR on DC triggered F-actin polymerization, indicating the chemotactic potential of DC elicited by C5a. C5a induced F-actin polymerization was increased when C5aR was up-regulated by PGE2. Stimulation of DC with C5a resulted in interleukin-10 production which was significantly increased after C5aR up-regulation with TNF-alpha and PGE2. Therefore, up-regulation of the C5aR on human DC alters their chemotactic and immunologic response to C5a.

Airway eosinophils accumulate in the mediastinal lymph nodes but lack antigen-presenting potential for naive T cells

Asthma is characterized by infiltration of the airway wall with eosinophils. Although eosinophils are considered to be effector cells, recent studies have reported their ability to activate primed Th2 cells. In this study, we investigated whether eosinophils are capable of presenting Ag to unprimed T cells in draining lymph nodes (DLN) of the lung and compared this capacity with professional dendritic cells (DC). During development of eosinophilic airway inflammation in OVA-sensitized and challenged mice, CCR3(+) eosinophils accumulated in the DLN. To study their function, eosinophils were isolated from the bronchoalveolar lavage fluid of mice by sorting on CCR3(+)B220(-)CD3(-)CD11c(dim) low autofluorescent cells, avoiding contamination with other APCs, and were intratracheally injected into mice that previously received CFSE-labeled OVA TCR-transgenic T cells. Eosinophils did not induce divisions of T cells in the DLN, whereas DC induced on average 3.7 divisions in 45.7% of T cells. To circumvent the need for Ag processing or migration in vivo, eosinophils were pulsed with OVA peptide and were still not able to induce T cell priming in vitro, whereas DC induced vigorous proliferation. This lack of Ag-presenting ability was explained by the very weak expression of MHC class II on fresh eosinophils, despite expression of the costimulatory molecules CD80 and ICAM-1. This investigation does not support any role for airway eosinophils as APCs to naive T cells, despite their migration to the DLN at times of allergen exposure. DC are clearly superior in activating T cells in the DLN of the lung.

Lipopolysaccharide-induced suppression of airway Th2 responses does not require IL-12 production by dendritic cells

The prevalence of atopic asthma, a Th2-dependent disease, is reaching epidemic proportions partly due to improved hygiene in industrialized countries. There is an inverse correlation between the level of environmental endotoxin exposure and the prevalence of atopic sensitization. As dendritic cells (DC) have been implicated in causing sensitization to inhaled Ag, we studied the effect of endotoxin on Th2 development induced by bone marrow DC in vitro and by intratracheal injection in vivo, with particular emphasis on the role played by the polarizing cytokine IL-12. Bone marrow-derived DC stimulated with Escherichia coli O26:B6 LPS produced IL-12p70 for a limited period of time, after which production became refractory to further stimulation with CD40 ligand, a phenomenon previously called "exhaustion." The level of IL-12 production of DC did not correlate with Th1 development, as exhausted OVA-pulsed DC were still capable of shifting the cytokine pattern of responding OVA-specific Th cells toward Th1 in vitro and in vivo. When mice were first immunized by intratracheal injection of OVA-DC and subsequently challenged with OVA aerosol, prior in vitro stimulation of DC with LPS reduced the development of airway eosinophilia and Th2 cytokine production. Most surprisingly, the capacity of LPS to reduce Th2-dependent eosinophilic airway inflammation was IL-12-independent altogether, as IL-12p40 knockout DC had a similar reduced capacity to prime for Th2 responses. These results suggest that LPS reduces sensitization to inhaled Ag by reducing DC-driven Th2 development, but that IL-12 is not necessary for this effect.

Prostaglandin D2 inhibits airway dendritic cell migration and function in steady state conditions by selective activation of the D prostanoid receptor 1

PGD(2) is the major mediator released by mast cells during allergic responses, and it acts through two different receptors, the D prostanoid receptor 1 (DP1) and DP2, also known as CRTH2. Recently, it has been shown that PGD(2) inhibits the migration of epidermal Langerhans cells to the skin draining lymph nodes (LNs) and affects the subsequent cutaneous inflammatory reaction. However, the role of PGD(2) in the pulmonary immune response remains unclear. Here, we show that the intratracheal instillation of FITC-OVA together with PGD(2) inhibits the migration of FITC(+) lung DC to draining LNs. This process is mimicked by the DP1 agonist BW245C, but not by the DP2 agonist DK-PGD(2). The ligation of DP1 inhibits the migration of FITC-OVA(+) DCs only temporarily, but still inhibits the proliferation of adoptively transferred, OVA-specific, CFSE-labeled, naive T cells in draining LNs. These T cells produced lower amounts of the T cell cytokines IL-4, IL-10, and IFN-gamma compared with T cells from mice that received FITC-OVA alone. Taken together, our data suggest that the activation of DP receptor by PGD(2) may represent a pathway to control airway DC migration and to limit the activation of T cells in the LNs under steady state conditions, possibly contributing to homeostasis in the lung.

Antigen presentation by local macrophages promotes nonallergic airway responses in sensitized mice

Local inflammatory responses involve relocating immune functions generated by previous immunization to confined parts of the body, and hence are presumed to reflect the prevailing systemic immune bias. To verify to what extent local antigen-presenting cells (APCs) may modulate immune inflammation, we analyzed the consequences of antigen presentation by macrophages on Th2-dependent airway inflammation in ovalbumin (OVA)-sensitized mice. In contrast to challenge with free OVA, which triggers airway eosinophilia and Th2 cell recruitment, intratracheal instillation of immortalized spleen macrophages (Mf4/4 cells), pulsed with OVA, promoted a nonallergic airway response featuring recruitment of interferon-gamma-producing Th1 cells. Combining OVA-Mf4/4 instillation with OVA inhalation strongly reduced airway eosinophilia. Inflammation repression persisted after secondary OVA challenge and depended on the antigen-presenting ability of the macrophages. Arguing against Th1-mediated counter-regulation, Th1/Th2 ratios remained unaltered in macrophage-treated/OVA-challenged mice. In contrast, levels of interleukin-4 and interleukin-13 mRNA in lung tissue CD4+ T cells were strongly downregulated, indicating a suppression of Th2 cell activation. These results document a role for local macrophages/APCs in controlling the nature and intensity of local immune inflammatory responses. The resulting segregation of systemic and local levels of immune reactivity may enable local inflammation tolerance; it is a nonallergic airway response despite systemic sensitization.

CD28/CTLA4 double deficient mice demonstrate crucial role for B7 co-stimulation in the induction of allergic lower airways disease

BACKGROUND

The existence of a third B7-1/B7-2 receptor was postulated in a recent study using a novel mouse strain lacking both CD28 and CTLA4 (CD28/CTLA4-/-).

OBJECTIVE

In the present study, it was investigated if T cell co-stimulation via the putative B7-1/B7-2 receptor plays a role in the induction of Th2-mediated asthma manifestations in mice.

METHODS

BALB/c wild-type, CD28/CTLA4-/- and B7-1/B7-2-/- mice were sensitized and aerosol challenged with ovalbumin (OVA).

RESULTS

At 24 h after the last aerosol, wild-type mice showed airway hyper-responsiveness in vivo and up-regulated levels of serum OVA-specific IgE compared with the situation shortly before OVA challenge. In addition, eosinophil numbers and IL-5 levels in the broncho-alveolar lavage fluid and Th2 cytokine production by lung cells upon OVA re-stimulation in vitro were observed. In agreement with an earlier study, we failed to induce any of the asthma manifestations in B7-1/B7-2-/- mice. Importantly, also CD28/CTLA4-/- mice showed no asthma manifestations upon OVA sensitization and challenge.

CONCLUSION

These data clearly demonstrate that T cell co-stimulation via the putative B7-1/B7-2 receptor appears to have no role in the induction of Th2-mediated asthma manifestations in this murine model and, conversely, that CD28 signalling is crucial.

Cloning and characterisation of a putative ST2L homologue from Atlantic salmon (Salmo salar)

The ST2L receptor is a member of the interleukin-1 (IL-1) receptor family and has previously been cloned from human, mouse, rat and chicken. This orphan receptor has no known physiological role but has been implicated in T helper cell type 2 effector function. We describe in this report the cloning and characterisation of a cDNA encoding a homologue of ST2L in Atlantic salmon (Salmo salar). The salmon ST2L cDNA is 2364bp in length and has an open reading frame encoding a polypeptide of 582 amino acids. Similar to other members of the IL-1 receptor (IL-1R) family, the predicted protein has a potential signal peptide, extracellular immunoglobulin-like domains, a short transmembrane region and a characteristic cytoplasmic Toll-IL-1R domain. The predicted protein shows 33% identity and 44% similarity to the chicken ST2L homologue. Phylogenetic analyses cluster the putative salmon ST2L with the chicken and the mammalian ST2L homologues, away from the other members of the IL-1R family. Salmon ST2L is constitutively expressed in brain, white and red blood cells, head kidney, liver, gills and muscle, with highest level of expression in spleen. In vivo stimulation of salmon with lipopolysaccaride does not appear to have a significant effect on expression of the ST2L homologue.

Accelerated airway dendritic cell maturation, trafficking, and elimination in a mouse model of asthma

Pulmonary dendritic cells (DC) can induce both tolerogenic as well as inflammatory immune responses in the lung. Conversely, little is known about the impact of ongoing airway inflammation on pulmonary DC biology. In noninflammatory conditions, expression of T cell costimulatory molecules on mouse airway DCs is low and only upregulated after homing into draining thoracic lymph nodes. In this study, we reveal that ongoing allergic airway inflammation induces a premature upregulation of the T cell costimulatory molecules CD40, B7-2 and intercellular adhesion molecule 1 on DCs still present in the airways. In contrast, high surface expression of inducible costimulator ligand, involved in respiratory tolerance induction is restricted to DCs from noninflamed lungs. In addition, during inflammation the migratory flux of allergen-transporting airway DCs toward draining thoracic nodes increases both in amplitude as well as in speed. Remarkably, migratory DCs from inflamed airways are short-lived in the draining lymph nodes, a finding that is temporally associated with a marked loss of the antiapoptotic protein Bcl-2 in these cells. This study demonstrates the profound effects of ongoing allergen-driven airway inflammation on the dynamics of pulmonary DC physiology, a knowledge that could be exploited in the development of novel DC-based immunotherapies.

Ribavirin or CpG DNA sequence-modulated dendritic cells decrease the IgE level and airway inflammation

Asthma is an allergic disease that is characterized by the imbalance between Th1 and Th2 cells and by the predominant Th2-type immune response. In this study, we investigated the application of dendritic cell (DCs)-based immunotherapy in modulating the immune response of allergic diseases. DCs incubated with ovalbumin (OVA), OVA plus ribavirin, OVA plus CpG-oligodeoxynucleotides (ODN 1826), or OVA plus non-CpG-ODN (ODN 1745) for 48 hours were injected intravenously into four corresponding groups of BALB/c mice. All of the mice were then immunized with OVA intraperitoneally 7 days later to establish an animal model of asthma. Serum levels of OVA antibody, airway hyperresponsivness, cell composition and cytokine levels in the bronchoalveolar lavage fluid, and cytokine profiles of spleen cells were analyzed. The data showed that ribavirin and ODN 1826 increased interleukin-12 synthesis and inhibited interleukin-10 production. ODN 1826 could also enhance the expression of B7.1, B7.2, major histocompatibility complex I, and major histocompatibility complex II molecules. Furthermore, the DCs modulated by ribavirin and ODN 1826 could downregulate the Th2-type immune response in vivo and could alleviate airway inflammation. This study elucidated the effect of ribavirin and CpG-ODN on DCs and demonstrated that in vitro modulated DCs might be a potential therapeutic approach for asthma.

Peroxisome proliferator-activated receptors alpha and gamma down-regulate allergic inflammation and eosinophil activation

Allergic asthma is characterized by airway hyperresponsiveness, eosinophilia, and mucus accumulation and is associated with increased IgE concentrations. We demonstrate here that peroxisome proliferator-activated receptors (PPARs), PPAR-alpha and PPAR-gamma, which have been shown recently to be involved in the regulation of various cell types within the immune system, decrease antigen-induced airway hyperresponsiveness, lung inflammation, eosinophilia, cytokine production, and GATA-3 expression as well as serum levels of antigen-specific IgE in a murine model of human asthma. In addition, we demonstrate that PPAR-alpha and -gamma are expressed in eosinophils and their activation inhibits in vitro chemotaxis and antibody-dependent cellular cytotoxicity. Thus, PPAR-alpha and -gamma (co)agonists might be of therapeutic interest for the regulation of allergic or inflammatory reactions by targeting both regulatory and effector cells involved in the immune response.

Matrix metalloproteinase-9-mediated dendritic cell recruitment into the airways is a critical step in a mouse model of asthma

Dendritic cells (DCs) appear to be strategically implicated in allergic diseases, including asthma. Matrix metalloproteinase (MMP)-9 mediates transmigration of inflammatory leukocytes across basement membranes. This study investigated the role of MMP-9 in airway DC trafficking during allergen-induced airway inflammation. MMP-9 gene deletion affected the trafficking of pulmonary DCs in a specific way: only the inflammatory transmigration of DCs into the airway lumen was impaired, whereas DC-mediated transport of airway Ag to the thoracic lymph nodes remained unaffected. In parallel, the local production of the Th2-attracting chemokine CC chemokine ligand 17/thymus and activation-regulated chemokine, which was highly concentrated in purified lung DCs, fell short in the airways of allergen-exposed MMP-9(-/-) mice. This was accompanied by markedly reduced peribronchial eosinophilic infiltrates and impaired allergen-specific IgE production. We conclude that the specific absence of MMP-9 activity inhibits the development of allergic airway inflammation by impairing the recruitment of DCs into the airways and the local production of DC-derived proallergic chemokines.

Airway dendritic cells: co-ordinators of immunological homeostasis and immunity in the respiratory tract

The large quantities and complex mixtures of antigens encountered daily at airway mucosal and alveolar surfaces pose a major challenge to maintenance of immunological homeostasis in the respiratory tract. Amongst this myriad of antigens, the immune system must discriminate between innocuous components that can be tolerated by the host and potentially life-threatening pathogens that require a rapid immune response. Dendritic cells (DC) represent the principal cell type at these sites capable of processing antigens and delivering signals that initiate tolerogenic or immunogenic immune responses. This review will discuss the role of DC at the "front-line" of immune surveillance and homeostasis within the respiratory tract and their role in the pathogenesis of respiratory disease.

The role of dendritic cells in immune regulation and allergic airway inflammation

Dendritic cells (DC) are potent antigen presenting cells that display an extraordinary capacity to present antigen to naïve T-cells and initiate primary immune responses. In the context of the lung and upper airway it is clear that DC play a key role in the regulation of adaptive immune responses to inhaled antigen. DC are particularly sensitive to signals derived from microbes, allergens and the airway tissue microenvironment. By the nature of the signals they provide at the time of antigen presentation, DC can polarize naïve T-cells into either T-helper type 1 (Th1) or Th2 effector cells, and are increasingly recognized as having a central role in the establishment of T-cell memory and peripheral immune tolerance. DC form a network within the upper airway and lung, and are rapidly recruited from the circulation in response to a variety of proinflammatory stimuli. Studies using animal models have highlighted the role of DC in both the initiation and maintenance of allergic airway inflammation. In early childhood, human DC are functionally immature, and this is thought to contribute to the development of allergic sensitization in those children who are genetically at risk for the development of atopy. Increased numbers of airway mucosal DC are found in both allergic rhinitis and asthma, while studies of blood-derived DC have emphasized important differences between the function of DC from atopic and normal individuals. This article reviews recent information on the involvement of DC in allergic airway disease, and the mechanisms by which DC could be exploited as targets for therapy in asthma and allergic rhinitis.

Protective effects of a recombinant fragment of human surfactant protein D in a murine model of pulmonary hypersensitivity induced by dust mite allergens

Lung surfactant protein D (SP-D) is a carbohydrate pattern recognition immune molecule. It can interact with a range of pathogens, stimulate immune cells and manipulate cytokine profiles during host's immune response. SP-D has also been shown to interact, via its carbohydrate recognition domains, with glycoprotein allergens of house dust mite (Dermatophagoides pteronyssinus, Derp), inhibiting specific IgE isolated from mite-sensitive asthmatic patients from binding these allergens, and blocking subsequent histamine release from sensitized basophils. In the present study, we have examined the protection offered by various doses of intranasal administration of a recombinant fragment of human SP-D (rhSP-D) in a murine model of pulmonary hypersensitivity to Derp allergens which showed characteristic high levels of specific IgE antibodies, peripheral blood eosinophilia, pulmonary infiltrates and a Th2 cytokine response. Treatment of Derp mice with rhSP-D led to significant reduction in Derp-specific IgE levels, blood eosinophilia and pulmonary cellular infiltration. The levels of IL-4 and IL-5 were decreased, while those of IL-12 and IFN-gamma were raised in the supernatant of the cultured splenocytes, indicating a Th2 to Th1 polarization. These results suggest that SP-D has a protective role in the modulation of allergic sensitization and in the development of allergic reactions to Derp allergens and highlight potential of the rhSP-D as a therapeutic for pulmonary hypersensitivity.

IL-6 production by pulmonary dendritic cells impedes Th1 immune responses

Mucosal tissues, such as the lung, are continually exposed to both foreign and environmental Ags. To counter the potential inflammatory tissue injury of chronic Th1-mediated responses against these Ags, mucosal sites may skew toward Th2 immune responses. However, the mechanism by which this occurs is unknown. Dendritic cells (DC), as orchestrators of the immune response, skew Th1/Th2 differentiation by cytokine secretion and expression of specific cell surface markers. We compared DC from mucosal and systemic locations. In this study, we show that the lung lacks a CD8alpha(+) DC subpopulation and contains DC that appear less mature than splenic DC. Furthermore, we demonstrate that pulmonary DC produce significant levels of IL-6 and fail to produce the Th1-polarizing cytokine IL-12. Importantly, we demonstrate that IL-6 negatively regulates IL-12 production, as pulmonary DC from IL-6(-/-) mice produce significant levels of IL-12 and induce Th1 polarization of naive CD4(+) T cells. Furthermore, we demonstrate that IL-6 is sufficient to explain the differential polarizing abilities of pulmonary and splenic DC, as splenic DC cocultures supplemented with IL-6 polarize naive T cells toward Th2, and pulmonary DC cultures in which IL-6 was removed with neutralizing Ab resulted in more Th1 polarization, pointing to IL-6 as the mechanism of Th2 polarization in the lung. We propose that the Th2 response seen in the lung is due to DC-mediated inhibition of Th1 responses via IL-6 production, rather than enhanced Th2 responses, and that this regulation decreases the likelihood of chronic inflammatory pathology in the lung.

Accelerated migration of respiratory dendritic cells to the regional lymph nodes is limited to the early phase of pulmonary infection

Respiratory dendritic cells (RDC) are believed to play a central role in the induction of adaptive immune responses to pulmonary infection. Herein we examine the basal migration of RDC from the lungs to secondary lymphoid tissues and their enhanced maturation/migration after pulmonary infection/inflammation. We demonstrate that the accelerated migration of RDC to the draining peribronchial lymph nodes occurs only during the first 24 hr after pulmonary virus infection. RDC are refractory to further migration thereafter in spite of ongoing virus replication and pulmonary inflammation. We further demonstrate that induction of this RDC refractory state suppresses additional RDC mobilization to subsequent pulmonary virus infection and results in concomitant suppression of an antiviral pulmonary CD8(+) T cell response.

The other cells in asthma: dendritic cell and epithelial cell crosstalk

Dendritic cells (DCs) and epithelial cells are the first cells to encounter inhaled allergens. The response of these cell types to allergens is fundamentally different in asthmatics compared with nonasthmatics. DCs and epithelial cells interact through cell-cell interactions and through release of soluble mediators. The response of epithelial cells to allergens can profoundly modify the behavior of intramucosal DCs. Upon migration to the draining nodes, mucosal DCs undergo functional maturation and induce proliferation in naive T cells and primed Th2 cells. The implications of the DC-epithelial interaction for the pathogenesis of asthma is becoming increasingly clear by the use of mouse models and culture systems of human cells.

Kinetics and mode of peptide delivery via the respiratory mucosa determine the outcome of activation versus TH2 immunity in allergic inflammation of the airways

BACKGROUND

Specific immunotherapy involving systemic injection of allergen, though highly effective, can cause severe side effects due to IgE-mediated activation of effector cells. Allergen-derived peptides might provide a safer alternative. We have investigated the use of mucosally delivered peptide to induce CD4(+) T(H)2 cell tolerance and thus protect against allergen-induced airway inflammation.

OBJECTIVE

The purpose of this study was to investigate whether intranasal administration of an allergen-derived peptide, either alone or adsorbed to chitosan, can prevent the induction of T(H)2-mediated pulmonary inflammation after sensitization and challenge of the airways with allergen.

METHODS

Mice were given (intranasally) a peptide containing an immunodominant epitope of the Dermatophagoides pteronyssinus (Der p) 1 allergen, either as soluble antigen or adsorbed to chitosan, before sensitization and allergen challenge. Pulmonary inflammation, antigen-specific CD4(+) T-cell responses, and antibody levels in sera were then determined.

RESULTS

Mice given peptide adsorbed to chitosan had significant reductions in airway eosinophilia, which correlated with reduced levels of IL-4 and IL-5 in the bronchoalveolar lavage fluid. There was decreased recruitment of activated CD4(+) T cells into the airways after allergen challenge, which correlated with a loss of Der p 1-specific T-cell cytokine responses in the periphery and the localized production of IL-10 by antigen-specific T cells in bronchial lymph nodes. Induction of peripheral T-cell tolerance was preceded by transient T-cell activation and IFN-gamma production.

CONCLUSION

Our data demonstrate that suppression of airway inflammation by intranasal administration of peptide antigen adsorbed to chitosan is initiated by transient T-cell activation and maintained by the production of IL-10 by antigen-specific T cells in the draining lymph nodes.

Cytokine memory of T helper lymphocytes

Memory is one of the key features of the adaptive immune system. Specific T and B lymphocytes are primed for a particular antigen and upon challenge with it will react faster than naive lymphocytes. They also memorize the expression of key effector molecules, in particular cytokines, which determine the type and scale of an immune reaction. While in primary activations differential expression of cytokine genes is dependent on antigen-receptor signaling and differentiation signals, in later activations the expression is triggered by antigen-receptor signaling and dependent on the cytokine memory. The molecular basis of the cytokine memory implies differential expression of transcription factors and epigenetic modifications of cytokine genes and gene loci. GATA-3 for Th2 and T-bet for Th1 cells expressing interleukin-4 or interferon-gamma, respectively, are prime candidates for key transcription factors of cytokine memory. The essential role of epigenetic modifications is suggested by the requirement of DNA synthesis for the establishment of a cytokine memory in Th lymphocytes. At present the molecular link between transcription factors and epigenetic modifications of cytokine genes in the establishment and maintenance of cytokine memory is not clear. The initial cytokine memory is not stable against adverse differentiation signals, while in repeatedly stimulated lymphocytes it is stabilized by a variety of mechanisms.

Allergen-induced accumulation of airway dendritic cells is supported by an increase in CD31(hi)Ly-6C(neg) bone marrow precursors in a mouse model of asthma

Airway dendritic cells (DCs) are held responsible for inducing sensitization to inhaled antigen, leading to eosinophilic airway inflammation, typical of asthma. However, less information is available about the role of these cells in ongoing inflammation. In a mouse model of asthma, sensitization to ovalbumin (OVA) was induced by intratracheal injection of myeloid OVA-pulsed DCs. Upon OVA aerosol challenge and induction of eosinophilic airway inflammation in sensitized mice, there was a time-dependent and almost 100-fold increase in the number of MHCII(+) CD11b(+) CD11c(+) endogenous airway DCs as well as CD11b(+) blood DCs. The mechanism of this increase was studied. Adoptive transfer experiments demonstrated that accumulation of airway DCs was not due to reduced migration to the mediastinal lymph nodes. Rather, the massive increase in airway and lymph node DCs was supported by an almost 3-fold expansion of myeloid CD31(hi)Ly-6C(neg) hematopoietic precursor cells in the bone marrow (BM). There was no change in any of the other 5 populations revealed by CD31/Ly-6C staining. When these CD31(hi)Ly-6C(neg) BM precursors were sorted and grown in granulocyte macrophage-colony-stimulating factor, they differentiated into MHCII(+) CD11c(+) DCs. The same CD31(hi)Ly-6C(neg) precursors also expressed the eotaxin receptor CCR3 and differentiated into eosinophils when grown in interleukin 5. Serum levels of eotaxin were doubled in mice with inflammation. These findings in an animal model of asthma suggest that the BM increases its output of myeloid precursors to meet the enhanced demand for DCs and eosinophils in inflamed airways.

Chronic exposure to innocuous antigen in sensitized mice leads to suppressed airway eosinophilia that is reversed by granulocyte macrophage colony-stimulating factor

In this study we investigated the impact of chronic allergen exposure on airway inflammation and humoral responses in sensitized mice. We observed marked eosinophilia in the bronchoalveolar lavage, lung tissue, and peripheral blood after 2 wk of exposure. In contrast, eosinophilia was markedly reduced by 3 wk and completely resolved by 4 wk of exposure, despite the continued presence of Ag. Decreases in airway eosinophilia were associated with a robust humoral response. We observed that levels of OVA-specific IgE, IgG1, and IgG2a increased during the course of exposure. To assess whether continuous exposure to Ag impacts the ability of the lung to respond to subsequent Ag challenge, mice were exposed to either 2 or 4 wk of OVA in the context of GM-CSF. All groups were then rested for 28 days and exposed to OVA on three consecutive days. We observed a significant decrease in airway eosinophilia and IL-5 expression in the bronchoalveolar lavage and serum in mice initially exposed to 4 wk of OVA, compared with animals exposed to 2 wk only. However, in both groups expression of B7.2 on dendritic cells as well as CD25, CD69, and T1/ST2 on CD4(+) T cells was enhanced, suggesting immune activation. Delivery of rGM-CSF fully restored airway eosinophilia. This study shows that exposure to innocuous Ag alone does not lead to persistent eosinophilic airway inflammation, but rather to abrogated eosinophilia. This suppression can be reversed by GM-CSF.

Involvement of the mannose receptor in the uptake of Der p 1, a major mite allergen, by human dendritic cells

BACKGROUND

Immature dendritic cells (DCs) take up antigens in peripheral tissues and, after antigen processing, mature to efficiently stimulate T cells in secondary lymph nodes. In allergic airway diseases DCs have been shown to be involved in the induction and maintenance of a T(H)2-type profile.

OBJECTIVE

The present study was undertaken to determine pathways of Der p 1 (a house dust mite allergen) uptake by human DCs and to compare Der p 1 uptake between DCs from patients with house dust mite allergy and DCs from healthy donors.

METHODS

Monocyte-derived DCs (MD-DCs) were obtained from patients with house dust mite allergy (n = 13) and healthy donors (n = 11). Der p 1 was labeled with rhodamine. Der p 1 uptake by MD-DCs was analyzed by means of flow cytometry and confocal microscopy.

RESULTS

Rhodamine- labeled Der p 1 was demonstrated to be taken up by MD-DCs in a dose-, time-, and temperature- dependent manner. The involvement of the mannose receptor (MR) in the Der p 1 uptake was demonstrated by using (1) inhibitors of the MR- mediated endocytosis (mannan and blocking anti-MR mAb), which inhibited the Der p 1 uptake from 40 % to 50 %, and (2) confocal microscopy showing the colocalization of rhodamine-labeled Der p 1 with FITC-dextran. Interestingly, compared with DCs from healthy donors, DCs from allergic patients expressed more MR and were more efficient in Der p 1 uptake.

CONCLUSION

These results suggest that the MR could play a key role in the Der p 1 allergen uptake by DCs and in the pathogenesis of allergic diseases in dust mite -sensitive patients.

The role of airway dendritic cell populations in regulation of T-cell responses to inhaled antigens: atopic asthma as a paradigm

Chronic atopic asthma in adulthood represents the end stage of a disease process that is initiated during the perinatal period, when the naive immune system is first confronted with potentially allergenic airborne antigens. The initial phase involves compartmentalization of immunological memory into either the T-helper (Th)-1 or Th2 cytokine phenotypes, in atopic and nonatopics, respectively, and in a subset of atopics, this results in chronic Th2 cytokine-driven inflammation in the airways. Dendritic cells appear to play a key role in directing the memory generation process, and in subsequently controlling the intensity and duration of the ensuing Th-cell responses responsible for this inflammation.